In a conventional recoding device that ejects recording liquid such as an inkjet recording device, a separate liquid cartridge is often used for supplying liquid to the recoding device. If there is a small amount of liquid left in the liquid cartridge when a user replaces the liquid cartridge, the liquid in the liquid cartridge will soon become empty if a large amount of printing is performed right after the replacement. In such a case, the user needs to replace the liquid cartridge again in the middle of the printing operation. In order to avid such a situation, there is a need for a configuration that detects whether the amount of liquid remaining in the liquid cartridge is small, and, if so, warns that the cartridge needs to be replaced soon.
For example, Japanese Patent Application Publication No. 2004-34406 (FIG. 2) discloses that a float is provided in a liquid cartridge so as to be dislocated in accordance with a decrease in the amount of liquid in the liquid cartridge. A degree of displacement of the float in a horizontal direction can be detected by a reflective optical sensor that moves horizontally relative to the liquid cartridge. This construction can detect how much liquid is left in the liquid cartridge as needed. Or alternatively, a plurality of optical sensors can be employed with respect to the horizontal direction, instead of moving an optical sensor, in order to detect residual amounts of liquid as in this patent reference. With these methods, detecting amounts of liquid left in a liquid cartridge right after the liquid cartridge is mounted may determine whether the remaining amount of liquid in the liquid cartridge is little.
However, if an optical sensor is configured to move relative to a liquid cartridge as disclosed in patent document 1, dimensions of a recoding device tend to be large. Moreover, providing a plurality of optical sensors leads to an increase in the number of parts. Hence, a liquid cartridge employing the above-described detecting methods necessitates an increase in costs of a recoding device.